Biasing Effects in Ferroic Materials

Abstract

In this chapter we present an overview of some important concepts related to the processes and microstructural mechanisms that produce the deformation of hysteresis loops and the loss of their symmetry characteristics in ferroelectric, ferroelastic and ferromagnetic systems. The most discussed themes include: aging and fatigue as primary mechanisms of biased hysteresis loops in ferroelectric/ferroelastic materials, imprint phenomenon as an important biasing process in ferroelectric thin films, the development of an exchange bias field and of specific spin states, such as spin canting and spin-glass-like phases, as the main causes of biased hysteresis loops in different types of magnetic heterostructures. The present discussion leads to the identification of the main differences and possible analogies in the underlying mechanisms of possible biasing effects occurring in the different ferroic systems, which can benefit the theoretical description, modelling, and engineering of multifunctional devices based on ferroic systems experiencing the internal bias phenomena.

Electrically Controlled Reversible Polarization Fatigue–Recovery in Ferroelectric Thin Film Capacitors

“…We held all measurement parameters constant throughout the experiment to rule out the influence of triangular signal voltage and frequency on remanent polarization. Observed asymmetry in P r+ and P r– values and the intrinsic imprint in hysteretic behavior indicate the existence of an internal bias or built-in field ( E bi ), where the half-sum of the measured coercive fields is used to compute E bi [ E bi = ( E c+ + E c– )/2]. , The magnitude of the E bi pointing toward the bottom electrode obtained from the imprint is ∼226 kV/cm.…”

“…Observed asymmetry in P r+ and P r− values and the intrinsic imprint in hysteretic behavior indicate the existence of an internal bias or built-in field (E bi ), where the half-sum of the measured coercive fields is used to compute E bi [E bi = (E c+ + E c− )/2]. 16,34 The magnitude of the E bi pointing toward the bottom electrode obtained from the imprint is ∼226 kV/cm. However, it should be noted that the built-in field calculations are quite illustrative but not optimal for qualitative characterization due to the difference in saturation at the tips of the loop introduced by the internal bias.…”

Relaxor-to-Ferroelectric Crossover and Disruption of Polar Order in “Empty” Tetragonal Tungsten Bronzes

“…[50][51][52][53][54] Thermal annealing above T C or applying 'de-aging' or fatiguing bipolar excitation cycles of sufficient field can reverse the mechanisms responsible for aged, defect-mediated pinched P-E loops in "normal" ferroelectrics. [55][56][57] Such measurements were performed on Ba 4 La 0.67 Nb 10 O 30 (see ESI Figures S12-S15 for details).…”

Unravelling and controlling hidden imprint fields in ferroelectric capacitors

“…Imprint fields can have different origins, such as asymmetric metal-dielectric interfaces, which may give rise to unequal Schottky barriers, or graded defect concentration 22 23 . Consequently, to reduce E imp , electrode-ferroelectric-electrode structures should be made as symmetric as possible 24 .…”